Turbo labs turn out good stuff. Anyone modifying/ building turbo cars have likely heard of them or used their products.
They are hard to get in touch with but, they’re busy making money. It seems they get roped into specific models and then kill it from there.
Tim’s turbos is another great turbo shop. They can modify your turbos. I run a set on my 335d. I picked up 100whp with their hybrid option with no loss in driveability.
http://www.timsturbos.com